8-Speed Transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets, six torque-transmitting devices, a split sun gear, two fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members, and the transmission housing, and are operated in combinations of two to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having three planetary gear sets controlled to provideeight forward speed ratios and one reverse speed ratio.

The transmission family of the present invention has three planetarygear sets, each of which includes a first, second and third member,which members may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order. One member of one of the planetary gearsets is split into two portions.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

One planetary gear set has a split first member consisting of a firstportion and a second portion, which enables a connection to the secondmember of the planetary gear set between the first and second portionsof the split first member.

A first interconnecting member continuously connects the second memberof the first planetary gear set with the third member of the secondplanetary gear set.

A second interconnecting member continuously connects the first memberof the first planetary gear set with the first member of the thirdplanetary gear set.

The third member of the first planetary gear set is continuouslyconnected to a stationary member (transmission housing/casing). Theinput member is continuously connected with the first portion of thesplit first member of the second planetary gear set. The output memberis continuously connected with the third member of the third planetarygear set.

A first torque-transmitting device, such a brake, selectively connectsthe second member of the third planetary gear set with a stationarymember (transmission housing/casing).

A second torque-transmitting device, such as a brake, selectivelyconnects the first member of the first planetary gear set with astationary member (transmission housing/casing).

A third torque-transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with thesecond member of the second planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with thesecond portion of the split first member of the second planetary gearset.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the second member of the second planetary gear set with thethird member of the third planetary gear set.

A sixth torque-transmitting device, such as a clutch, selectivelyconnects the second portion of the split first member of the secondplanetary gear set with the second member of the third planetary gearset.

The six torque-transmitting devices are selectively engageable incombinations of two to yield eight forward speed ratios and one reversespeed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. I adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes first and second split sun gearmember portions 320, 321, a ring gear member 34, and a planet carrierassembly member 36. The planet carrier assembly member 36 includes aplurality of pinion gears 37 rotatably mounted on a carrier member 39and disposed in meshing relationship between the first and second splitsun gear member portions 320, 321 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes six torque-transmittingdevices 50, 52, 54, 55, 56 and 57. The torque-transmitting devices 50and 52 are stationary-type torque-transmitting devices, commonly termedbrakes or reaction clutches. The torque-transmitting devices 54, 55, 56and 57 are rotating-type torque-transmitting devices, commonly termedclutches.

The input member 17 is continuously connected with the split sun gearmember portion 320 of the planetary gear set 30. The output member 19 iscontinuously connected with the ring gear member 44 of the planetarygear set 40. The ring gear member 24 is continuously connected with thetransmission housing 60.

A first interconnecting member 70 continuously connects the planetcarrier assembly member 26 with the ring gear member 34. A secondinterconnecting member 72 continuously connects the sun gear member 22with the sun gear member 42.

A first torque-transmitting device, such as brake 50, selectivelyconnects the planet carrier assembly member 46 with the transmissionhousing 60. A second torque-transmitting device, such as brake 52,selectively connects the sun gear member 22 and the sun gear member 42via interconnecting member 72 with the transmission housing 60. A thirdtorque-transmitting device, such as clutch 54, selectively connects thesun gear member 22 with the planet carrier assembly member 36. A fourthtorque-transmitting device, such as clutch 55, selectively connects thesun gear member 22 with the split sun gear member portion 321. A fifthtorque-transmitting device, such as clutch 56, selectively connects theplanet carrier assembly member 36 with the ring gear member 44. A sixthtorque-transmitting device, such as clutch 57, selectively connects thesun gear member 321 with the planet carrier assembly member 46.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of two to provide eight forward speed ratios and onereverse speed ratio, all with single transition shifts and with a doubleoverdrive.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.61, while the step ratio between the reversespeed ratio and first forward ratio is −0.60.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format.

The powertrain 10 includes an input member 17, an output member 19, afirst planetary gear set 20A having three nodes: a first node 22A, asecond node 26A and a third node 24A; a second planetary gear set 30Ahaving three nodes: a first node 32A (corresponding with elements 320and 321 of FIG. 1 a), a second node 36A and a third node 34A; a thirdplanetary gear set 40A having three nodes: a first node 42A, a secondnode 46A and a third node 44A.

The input member 17 is continuously connected with the node 32A. Theoutput member 19 is continuously connected with the node 44A. The node24A is continuously connected with the transmission housing 60.

The node 26A is continuously connected with the node 34A viainterconnecting member 70. The node 22A is continuously connected withnode 42A via interconnecting member 72.

A first torque-transmitting device, such as brake 50 engages the node46A with the transmission housing 60. A second torque-transmittingdevice, such as brake 52, engages the nodes 22A and 42A viainterconnecting member 72 with the transmission housing 60. A thirdtorque-transmitting device, such as clutch 54, engages the nodes 22A and42A via interconnecting member 72 with the node 36A. A fourthtorque-transmitting device, such as clutch 55, engages the nodes 22A and42A via interconnecting member 72 with the node 32A. A fifthtorque-transmitting device, such as clutch 56, engages the node 36A withthe node 44A. A sixth torque-transmitting device, such as clutch 57,engages the node 32A with the node 46A.

To establish ratios, two torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row of FIG. 1 b. For example, to establishreverse gear, the brake 50 and clutch 55 are engaged. The brake 50engages the node 46A with the transmission housing 60. The clutch 55engages the nodes 22A and 42A with the node 32A. Likewise, the eightforward ratios are achieved through different combinations of clutchengagement as per FIG. 1 c.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members and wherein the first member of one of saidplanetary gear sets is split into first and second portions; a firstinterconnecting member continuously connecting said second member ofsaid first planetary gear set with said third member of said secondplanetary gear set; a second interconnecting member continuouslyconnecting said first member of said first planetary gear set with saidfirst member of said third planetary gear set; said third member of saidfirst planetary gear set being continuously connected with a stationarymember; and six torque-transmitting devices for selectivelyinterconnecting said members of said planetary gear sets with saidstationary member or with other members of said planetary gear sets,said six torque-transmitting devices being engaged in combinations oftwo to establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member. 2.The transmission of claim 1, wherein a first of said sixtorque-transmitting devices is operable for selectively connecting saidsecond member of said third planetary gear set with said stationarymember.
 3. The transmission of claim 2, wherein a second of said sixtorque-transmitting devices is operable for selectively connecting saidfirst member of said first planetary gear set with said stationarymember.
 4. The transmission of claim 3, wherein a third of said sixtorque-transmitting devices is operable for selectively connecting saidfirst member of said first planetary gear set with said second member ofsaid second planetary gear set.
 5. The transmission of claim 4, whereina fourth of said six torque-transmitting devices is operable forselectively connecting said first member of said first planetary gearset with said second portion of said first member of said secondplanetary gear set.
 6. The transmission of claim 5, wherein a fifth ofsaid six torque-transmitting devices is operable for selectivelyconnecting said second member of said second planetary gear set withsaid third member of said third planetary gear set.
 7. The transmissionof claim 6, wherein a sixth of said six torque-transmitting devices isoperable for selectively connecting said second portion of said firstmember of said second planetary gear set with said second member of saidthird planetary gear set.
 8. The transmission defined in claim 1,wherein said first and second torque-transmitting devices comprisesbrakes, and said third, fourth, fifth and sixth torque-transmittingdevices comprise clutches.
 9. The transmission of claim 1, wherein saidfirst, second and third members of said first, second and thirdplanetary gear sets comprise a sun gear member, a planet carrierassembly member and a ring gear member, respectively.
 10. Thetransmission of claim 1, wherein said input member is continuouslyconnected with said first portion of said first member of said secondplanetary gear set; and said output member is continuously connectedwith said third member of said third planetary gear set.
 11. Thetransmission of claim 1, wherein a connection to one of saidtorque-transmitting devices extends between said first and secondportions of said split first member.
 12. A multi-speed transmissioncomprising: an input member; an output member; first, second and thirdplanetary gear sets each having first, second and third members andwherein the first member of one of said planetary gear set is split intofirst and second portions thereby allowing said second member of saidone of said planetary gear sets to be selectively connected to othermembers of said one planetary gear sets between said first and secondportions; said input member being continuously connected with said firstportion of said first member of said second planetary gear set; saidoutput member being continuously connected with said third member ofsaid third planetary gear set; a first interconnecting membercontinuously connecting said second member of said first planetary gearset with said third member of said second planetary gear set; a secondinterconnecting member continuously connecting said first member of saidfirst planetary gear set with said first member of said third planetarygear set; said third member of said first planetary gear set beingcontinuously connected with a stationary member; a firsttorque-transmitting device selectively connecting said second member ofsaid third planetary gear set with said stationary member; a secondtorque-transmitting device selectively connecting said first member ofsaid first planetary gear set with said stationary member; a thirdtorque-transmitting device selectively connecting said first member ofsaid first planetary gear set with said second member of said secondplanetary gear set; a fourth torque-transmitting device selectivelyconnecting said first member of said first planetary gear set with saidsecond portion of said first member of said second planetary gear set; afifth torque-transmitting device selectively connecting said secondmember of said second planetary gear set with said third member of saidthird planetary gear set; a sixth torque-transmitting device selectivelyconnecting said first member of said second planetary gear set with saidsecond member of said third planetary gear set; and said sixtorque-transmitting devices being engaged in combinations of two toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.
 13. Thetransmission of claim 12, wherein said first, second and third membersof said first, second and third planetary gear sets comprise a sun gearmember, a planet carrier assembly member and a ring gear member,respectively.
 14. A multi-speed transmission comprising: an inputmember; an output member; first, second and third planetary gear setseach having a sun gear member, planet carrier assembly member and ringgear member and wherein the sun gear member of said second planetarygear set is split into first and second portions thereby allowing saidplanet carrier assembly member of said second planetary gear set to beselectively connected to other members of said planetary gear setsbetween said first and second portions; said input member beingcontinuously interconnected with said first portion of said sun gearmember of said second planetary gear set; said output member beingcontinuously interconnected with said ring gear member of said thirdplanetary gear set; said ring gear member of said first planetary gearset being continuously connected with a stationary member; a firstinterconnecting member continuously connecting said planet carrierassembly member of said first planetary gear set with said ring gearmember of said second planetary gear set; a second interconnectingmember continuously connecting said sun gear member of said firstplanetary gear set with said sun gear member of said third planetarygear set; a first torque-transmitting device selectively connecting saidplanet carrier assembly member of said third planetary gear set withsaid stationary member; a second torque-transmitting device selectivelyconnecting said sun gear member of said first planetary gear set withsaid stationary member; a third torque-transmitting device selectivelyconnecting said sun gear member of said first planetary gear set withsaid planet carrier assembly member of said second planetary gear set; afourth torque-transmitting device selectively connecting said sun gearmember of said first planetary gear set with said second portion of saidsun gear member of said second planetary gear set; a fifthtorque-transmitting device selectively connecting said planet carrierassembly member of said second planetary gear set with said ring gearmember of said third planetary gear set; a sixth torque-transmittingdevice selectively connecting said second portion of said sun gearmember of said second planetary gear set with said planet carrierassembly member of said third planetary gear set; said sixtorque-transmitting devices being engaged in combinations of two toestablish eight forward speed ratios and one reverse speed ratio betweensaid input member and said output member.